Watershed Delineation for combined lake open-channel flow drainage

[PeterParker5]

Hello,

i posted a similar question a few days ago but I want to try it this way again.

given data:
DEM
drainage network
lakes

I'm trying to delineate catchments for an urban watershed whichs drainage consists mainly of open-channel flow. The open channels are connected to a larger number of lakes.
My current problem is that most of the lakes and drains are not represented in the DEM. The general elevation in my catchment is low and doesn't vary much (2-6 m.a.s.l), some parts are even below sea level. When I use DEM reconditioning I get negative elevation values for larger parts of my drainage. If I apply Fill Sinks my burnt streams are filled up again & the resulting watersheds and drainage lines don't match what I want to see.

As my streams run through a couple of lakes I want to represent them also in the DEM. How would I do that?
When I use Create Sink Structure I just identify them as a polygon but I dont burn them into the dem, right?

I found the workflow for Combined dendritic/deranged terrain with known sink and stream locations 
(yellow.esri.com - /archydro/archydro/) which might work in my case also, but I don't know how to overcome the issue that fill sinks always sort of recreates my initial dem with just slight changes. Most of my burnt streams are not recognizable anymore. If I use Fill Sinks with a threshold instead of Fill All I dont get the general eight flow direction (d8) output, but number from 1-255.

I have been searching through many Q&A, discussions and videos, but I couldnt find any detailed description or procedure of how to overcome this issue. I'd highly appreciate hints on representing the drains and lakes properly in the DEM & adjusting the flow direction.

cheers,
Peter

[DeanDjokic]

Arc Hydro answers

GeoNet – Peter Parker – 11/15/18

Peter,

In Arc Hydro parlance, lakes are polygons that are drained by the river. They are not sinks that “stop” the water. So you would use a variation of dendritic terrain processing to make it all work (Use Case 8 or 9 in the doc you are referring to). Deranged processing methods would be used if you have “real” sinks where the water enters but does not exit. Before you start, make sure that:

1. Your stream network is fully connected and has at least one stream segment that “exits” the DEM extent (that should be your watershed outlet stream segment). You cannot have “broken” stream lines that are not connected or not exiting the DEM. If you do, these will just be filled back after you burn them and you will most likely lose their definition.  (See attached figure).
2. Lake polygons have stream lines flowing out of them (it is OK if they do not flow into the lake – these would be lakes that originate streams).

Then the modified dendritic processing workflow involves running tool “Adjust Flow Direction in Lakes” BEFORE performing “Catchment Grid Delineation”. For:

1. Use case 8 (using synthetic streams) that is AFTER step 8 – “Drainage Line Processing”.
2. Use case 9 (using user specified streams) that is AFTER step 6 – “Adjust Flow Direction in Streams”.

Running “Adjust Flow Direction in Lakes” forces the water that flows into the lake to be directed into the stream that drains the lake, so all the flow paths from within the lake will come out from a single lake outlet. The algorithm we are using directs any cell within the lake to “flow” to the nearest stream cell within that lake. Depending on the shape of the lake and the stream within it, you might get some “unnatural” looking results.

 Hope this helps.

 Dean